In recent years, the products using the liquid crystal display (LCD) has become very popular, such as notebook computers, monitors, mobile phones cameras, LCD TVs, digital cameras and personal digital assistants (PDA), etc. Their applications can be easily found everywhere. Since the LCD cannot luminesce itself, the function of the backlight module is to provide the light source, which can provide sufficient brightness and uniform light distribution on the LCD panel. Therefore, the backlight module is actually inevitable equipment for the LCD products. Furthermore, the backlight module will still be a suitable choice in the other applied field of luminescent requirement even if it is not applied to the LCD products.
Traditionally, liquid crystal displays use the Cold Cathode Fluorescent Tube (CCFT) as their backlight light source, which emits white light. Since the CCFT with small diameter is very difficult to manufacture, the CCFT is restricted to be applied in liquid crystal display device of small electronic products. Moreover, the CCFT also has some drawbacks of high voltage requirement, large power consumption, electromagnetic interference and other environmental protection issues caused by the use of mercury.
Therefore, the light Emitting Diode (LED) has been developed as the backlight light source of the LCD. The LED backlight light source module can generally be divided into two types. One type is using a white LED as the backlight light source, but the cost of the white light LED is high, and the other type is using the LED of red, green and blue (RGB) colors as the backlight light source, which mixes the primary colors red, green and blue light emitted by the RGB tri-color LED and then produces the white light. When the RGB tri-color LED is used as the backlight light source, the backlight module of the LCD needs additional optical components or extra space to mix red, green and blue light.
The LED light source will have a great help for the LCD products because the light-emitting efficiency of LED has been dramatically improved. It is generally believed that the LED at the present stage has already possessed about half of efficiency of the CCFT. Even by year 2010, the LED light-emitting efficiency is expected to keep pace with the CCFT, of course, which is just in terms of brightness on the LED.
If the high response rate of the LED characteristics is applied, so as to sequentially light up the red, blue and green LED light source with high-speed switching, which is capable to not only replace high-priced color filters in the LCD panel, but also enhance color saturation and brightness of the liquid crystal display products. In view of this, the impact of future developing trends of LED light source for LCD display products will be comprehensive and thorough. In addition to the application in the liquid crystal display products, once the LED light-emitting performance is competitive to (or exceed) CCFT, their application would then be more extensive. For example, LED light is now used in many signal sources, such as traffic signals and the turn signals of cars. If the LED luminous performance makes further progress, the most likely application is to extend to the illumination light source. The LED which has the low power consumption and low-heating characteristics will bring a huge threat to the entire present lighting source.
FIG. 1 is a cross-section diagram of the conventional LED backlight system. As shown in FIG. 1, the backlight system includes plural light sources 10, a reflector 11, a mixing light guide plate 12, a mirror 13 and a main light guide plate 14. Among them, the light source 10 is configured in a row, and the light source 10 includes RGB tri-color LED. One LED is showed in the cross-section diagram of FIG. 1. The red, green and blue lights emitted from the light source 10 reflect to the mixing light guide plate 12 via the reflective mirror 11. Then, the red, green and blue lights change their direction through the reflective surface of the mixing light guide plate 12. Thus, the red, green and blue lights can be fully mixed into the white light by changing their direction in the mixing light guide plate 12. Then, the mixed white light is emitted by the mixing light guide plate 12 and reflected to the main light guide plate 14 via the reflective mirror 13. The mixed white light is transferred into the surface light source by the main light guide plate 14, and then, the mixed white light is sent to the optical components of the back-end and finally to the LCD panel.
However, in the above-mentioned prior art, due to the characteristic of light straight transmission, the light direction won't be changed until the light come into contact with the reflective surface of the mixing light guide plate 12. Therefore, if red, green and blue lights need to be fully mixed, the length of the mixing light guide plate 12, which is the path of the mixing light, must be long enough.
Based on the above description of the prior art, the LED backlight module needs a good light mixing mechanism to render the LED backlight module providing a uniform color mixing and brightness. However, the light mixing mechanism provided by the conventional LED backlight module as shown in FIG. 1 still has to be improved. In addition, while providing the LED backlight module with a better light mixing mechanism, it still has to consider the LED is a directional component, so as to avoid lowering the overall luminous efficiency of the LED backlight module while achieving a good light mixing effect.
Accordingly, it still lacks a LED backlight module having both light-emitting efficiency and mixing light effectiveness to overcome the imperfect shortcoming of light mixing effect in prior art. And the newly developed technology is expected to not only improve the mixing light effect, but also be quickly and easily integrated into the existing manufacturing process of the LED backlight module for facilitating the competitiveness of the industry in cost and other aspects.
Thus, the R & D personnel engaged in the related fields of the LED backlight modules are devoted to solve the shortcomings that still existed in the prior art, and further improve the quality of the LED backlight module products.